The implementation of beta-silicon carbide (3C-SiC) in the fabrication of semiconductor devices has been very limited to date. As is well known, SiC has a wide bandgap (2.2 eV for 3C-SiC and 3 eV for 6H-SiC) and high melting point (2800.degree. C.). This makes SiC an excellent semiconductor material for high temperature applications with 6H-SiC being the material of choice in most applications. This remains the case even though the cost of using 3C-SiC is significantly less than that of 6H-SiC.
The preference for 6H-SiC results from essentially two major problems associated with semiconductor devices fabricated from 3C-SiC. The first problem relates to the high amount of leakage current from the metallurgical pn junctions that is not expected from such a large bandgap material. More specifically, the pn junctions formed in 3C-SiC leak current 100-1000 times as much as a silicon pn junction. The other problem that semiconductor devices fabricated from 3C-SiC exhibit is an extremely low surface mobility. This problem is also associated with semiconductor devices fabricated from 6H-SiC. The extremely low surface mobility exhibited by SiC semiconductor devices is believed to be cause by the poor quality of the silicon dioxide (oxide) formed on SiC, and the poor interfacing between the oxide and the bulk SiC.
The first of these two problems is by far the most significant since most integrated circuit devices require one or more metallurgical pn junctions in reverse bias to function and isolate the devices from the surrounding circuitry. The second problem mainly impacts the circuit density that can be achieved, and this in turn impacts the cost of manufacturing. More specifically, a greater circuit density can be achieved with a high mobility semiconductor material than with a low mobility semiconductor material. This is because in order for the device to support a given amount current, the device made from the low mobility semiconductor material must have a channel width that is the ratio of the high to low mobilities multiplied by the channel width of the high mobility device. This invention overcomes both of these restrictions.
It is, therefore, a primary object of the present invention to provide a dielectrically isolated P-MOSFET device which substantially overcomes and eliminates the problems described above.